This week Opportunity demonstrated the challenges of operating a vehicle on the surface of another planet. The rover is en route to Cape Verde to acquire high-resolution images of the layering in the rocks. To get there, Opportunity must cross some sandy stretches. Before entering the sandy areas, Opportunity will need to stop and take a "toe dip'' -- that is, drive forward a short distance and back out again -- to characterize the terrain.

On Sol 1491 (April 3, 2008), Opportunity performed a 4-wheel toe dip, driving forward until the front four wheels were on the sand and backing up again.

As part of ensuring vehicle safety, rover drivers set conservative limits on what the rover may do. For example, if Opportunity exceeds the maximum amount of wheel slippage or the maximum amount of tilt allowed, the rover must abort the drive. This gives the rover's handlers a chance to further evaluate the situation and make changes to the drive plan on subsequent sols (Martian days). The toe dips provide valuable insight into the nature of the terrain Opportunity is likely to encounter on the way to Cape Verde.

Opportunity is healthy and all subsystems are performing as expected.

Sol-by-sol summary

In addition to receiving morning instructions directly from Earth via the rover’s high-gain antenna, sending data back to Earth via the UHF antenna on the Mars Odyssey orbiter, and measuring atmospheric dust with the panoramic camera, Opportunity completed the following activities:

Sol 1491 (April 3, 2008): Before the day's drive, Opportunity took panoramic-camera and navigation-camera images of a previously made wheel scuff. The rover stowed the robotic arm and drove toward Cape Verde, taking hazard avoidance-camera images before and after ending the drive. Opportunity unstowed the robotic arm and acquired post-drive images with the navigation and panoramic cameras.

Sol 1492: In the early part of the sol, Opportunity took spot images of the sky for calibration purposes and surveyed the horizon with the panoramic camera.

Sol 1493: Opportunity monitored dust on the panoramic-camera mast assembly, stowed the robotic arm, and continued driving toward Cape Verde. Just before and after ending the drive, Opportunity took images of the area close to the rover with the hazard-avoidance cameras. The rover unstowed the robotic arm, took post-drive images with the navigation camera, and after communicating with Odyssey, obtained measurements of argon gas in the Martian atmosphere using the alpha-particle X-ray spectrometer.

Sol 1494: Opportunity took thumbnail images of the sky with the panoramic camera and six movie frames in search of clouds with the navigation camera.

Sol 1495: Opportunity took spot images of the sky for calibration purposes with the panoramic camera, stowed the robotic arm, and drove toward Cape Verde. Before and after ending the drive, the rover took images with the hazard-avoidance cameras. Opportunity unstowed the robotic arm (known to engineers as the instrument deployment device) and acquired post-drive images with the navigation camera.

Sol 1496: In the morning, Opportunity took spot images of the sky for calibration purposes with the panoramic camera and shot a 4-frame movie in search of clouds with the navigation camera. Opportunity stowed the robotic arm and drove backward onto bedrock to extract its wheels from the sand before proceeding toward Cape Verde. Before and after ending the day's drive, the rover took images with the hazard-avoidance cameras. The rover then unstowed the robotic arm.

Sol 1497 (April 9, 2008): In the morning, Opportunity took thumbnail images of the sky with the panoramic camera and shot another 4-frame movie in search of clouds with the navigation camera. The rover acquired diagnostic images with the hazard-avoidance cameras and a mosaic of images of the work volume reachable by the robotic arm with the panoramic camera. When the evening Sun was low, Opportunity surveyed the sky with the panoramic camera. Plans transmitted to the rover for the following morning called for another 6-frame movie of potential clouds in the Martian sky.

Daily Update - 4/21/08Spirit Still 'Sitting Pretty' for This Time of Year
Spirit Status for sol 1517-1524

Despite a slight increase in atmospheric opacity caused by dust, Spirit is still enjoying higher-than-expected energy levels for this time of year. Solar array input has been approximately 240 watt-hours per Martian day, or sol (100 watt-hours is the amount of energy needed to light a 100-watt bulb for one hour).

Clear skies have had the unfavorable effect, however, of causing a drop in temperatures at the surface of Mars, increasing the bitter cold experienced by Spirit's rover electronics module. Nighttime temperatures are creeping closer to the point where they will trigger the survival heaters, which draw a large amount of power. A much more desirable strategy is to keep Spirit awake long enough each day to keep the electronics module sufficiently warm with heat from normal operations, providing more time for science observations. "Awake time" vs. heating time is just one of the many trade-offs the team makes each day to keep Spirit going through the Martian winter.

Sol-by-sol summary

In addition to daily communications that include direct-from-Earth instructions via the rover's high-gain antenna and, as power permits, data relays to Earth via the Odyssey orbiter, Spirit continues to monitor atmospheric dust levels each day with the panoramic camera. In addition, during the past week, Spirit completed the following activities:

Sol 1517 (April 9, 2008): Spirit completed a mini-survey of the sky and ground with the miniature thermal emission spectrometer; acquired column 8, part 3 of the full-color "Bonestell Panorama" using all 13 filters of the panoramic camera; and shot movie frames in search of clouds with the navigation camera.

Sol 1518: Spirit completed a mini-survey of the sky and ground with the miniature thermal emission spectrometer; acquired a 2-by-1-by-1 stack of microscopic images of the rover's solar array; acquired column 9, part 1 of the Bonestell panorama; and took spot images of the sky for calibration purposes with the panoramic camera.

Sol 1519: Spirit surveyed the rover's external calibration target with the miniature thermal emission spectrometer and acquired column 9, part 2 of the Bonestell panorama. To conserve energy, the rover did not relay data to Odyssey.

Sol 1520: Spirit completed a mini-survey of the sky and ground with the miniature thermal emission spectrometer; measured atmospheric opacity caused by dust with the navigation camera (as well as the panoramic camera); and acquired movie frames in search of clouds with the navigation camera. The rover took spot images of the sky and surveyed the horizon with the panoramic camera. Spirit did not relay data to Odyssey.

Sol 1521: Spirit completed a mini-survey of the sky and ground with the miniature thermal emission spectrometer; calibrated the elevation of the miniature thermal emission spectrometer; and acquired column 9, part 3 of the Bonestell panorama.

Sol 1522: Spirit completed a mini-survey of the sky and ground with the miniature thermal emission spectrometer; took thumbnail images of the sky and surveyed the horizon with the panoramic camera; and acquired lossless-compression images of wind-blown deposits next to the rover with the hazard-avoidance cameras. Spirit did not relay data to Odyssesy.

Sol 1523: Spirit recharged the battery and did not relay data to Odyssey.

Sol 1524: (April 16, 2008): Spirit recharged the battery.

Odometry

As of sol 1524 (April 16, 2008), Spirit’s total odometry remained at 7,528.07 meters (4.68 miles).

Opportunity has begun the drive toward a spectacular cliff in the wall of "Victoria Crater" known as "Cape Verde," about 30 meters (98 feet) away. The rover is expected to complete the drive in 6 to 7 segments, each covering an average distance of 5 meters (16 feet).

Along the way are several sandy patches. Before entering these sandy areas, Opportunity will stop for a "toe dip" -- a scuff with the front wheels to assess the depth of the sand. Rover planners hope the sandy spots will turn out to be bedrock with only a sandy veneer.

Opportunity executed the first of the toe dips upon arriving at a sandy patch on Sol 1489 (April 1, 2008). The scuff was successful. Electrical currents indicated that despite relatively deep sand on both sides, the wheels had good purchase. The sand was 4 centimeters (1.5 inches) deep on the left and 6 to 8 centimeters (2 to 3 inches) deep on the right. The tilt of the rover indicated that the left wheel encountered rock quickly, experiencing large vibrations after a short, smooth period. The right wheel got into deep sand after only brief contact with rock. Wheel slip and bogie (wheel suspension) angles indicated the rover moved backward about 3 centimeters (1 inch) during the scuffing. Rover planners concluded that the terrain was drivable but required caution.

Opportunity remains healthy and all subsystems are performing as expected. Energy is around 360 watt-hours (100 watt-hours is the amount of energy needed to light a 100-watt bulb for one hour). As of sol 1490 (April 2, 2008), Tau measurements of atmospheric opacity caused by dust stood at 0.65. The dust factor, a measure of the proportion of sunlight penetrating dust on the solar arrays, stood at 0.69.

Power may fluctuate slightly as Opportunity continues the drive toward the Cape Verde promontory, depending on the slopes of the local terrain and the rover's attitude relative to the Sun.

Sol-by-sol summary

In addition to receiving morning instructions directly from Earth via the rover’s high-gain antenna, sending data back to Earth via the UHF antenna on the Mars Odyssey orbiter, measuring atmospheric dust with the panoramic camera, monitoring dust accumulation on the rover mast, and surveying the sky for clouds with the navigation camera, Opportunity completed the following activities:

Sol 1484 (March 27, 2008): Opportunity began the drive to Cape Verde, advancing 5.55 meters (18.2 feet) and pausing midway through the drive to take full-color images, using all 13 filters of the panoramic camera, of the hole in the Gilbert rock layer created with the rover's rock abrasion tool. After the drive, Opportunity acquired a 3-by-1 mosaic of images with the navigation camera and a 3-by-2 mosaic of images with the panoramic camera. The rover went into a deep sleep.

Sol 1485: After relaying data to Odyssey, Opportunity spent six hours using the alpha-particle X-ray spectrometer to measure argon gas in the Martian atmosphere and went into a mini-deep sleep.

Sol 1487: Opportunity acquired six movie frames in search of clouds with the navigation camera and a 6-by-3 mosaic of the base of the Cape Verde cliff. After relaying data to Odyssey, Opportunity spent six hours measuring atmospheric argon and went into a mini-deep sleep.

Sol 1488: Opportunity acquired six movie frames in search of clouds with the navigation camera, recharged the battery, and went into a deep sleep.

Sol 1490 (April 2, 2008): Opportunity acquired a 5-by-1 tier of shadow images of Cape Verde, recharged the battery, and went into a deep sleep. Plans for the following morning called for the rover to take thumbnail images of the sky for calibration purposes with the panoramic camera.

Spirit is currently experiencing the clearest skies seen by either of NASA's two Mars Exploration Rovers. On sol 1511 (April 3, 2008), Tau measurements of atmospheric dust hit an all-time low of 0.127. By sol 1516 (April 8, 2008), this measurement had increased slightly to 0.170. The low Tau values have held power levels at around 250 watt-hours (enough energy to light a 100-watt bulb for about 2.5 hours). If Tau were not so cooperative, Spirit would be getting only about 200 watt-hours of energy, compelling the rover's handlers to disable the heaters on the miniature thermal emission spectrometer and take other measures to conserve power.

The engineering team still expects to implement energy-conservation strategies, but not for several weeks. Meanwhile, Spirit continues to make progress on remote-sensing activities, scientific investigations, and the "Bonestell panorama" of the rover's view from the north rim of "Home Plate."

Sol-by-sol summary

To conserve energy, mission planners have restricted the number of sols on which Spirit receives direct-from-Earth instructions via the rover's high-gain antenna and transmits data to Earth via the Odyssey orbiter. Spirit continues, on a daily basis, to monitor atmospheric dust levels with the panoramic camera and survey the sky and ground with the miniature thermal emission spectrometer. In addition, during the past week, Spirit completed the following activities:

Sol 1511 (April 3, 2008): Spirit took thumbnail images of the sky with the panoramic camera.

Sol 1512: Spirit gathered compositional data from the soil target known as "Arthur C. Harmon" using the alpha-particle X-ray spectrometer. The rover used the panoramic camera to acquire super-resolution images of a target informally named "Arthur C. Clarke."

Sol 1513: Spirit acquired column 7, part 3 of the full-color Bonestell panorama, using all 13 filters of the panoramic camera.

Sol 1514: Spirit pointed the alpha-particle X-ray spectrometer skyward to measure argon gas in the Martian atmosphere and acquired stability images of the rover's 30-degree tilt. The rover transmitted data to Odyssey and spent about 4.5 hours measuring atmospheric argon. Spirit also acquired column 8, part 1 of the Bonestell panorama and took spot images of the sky for calibration purposes with the panoramic camera.

Sol 1515: Spirit surveyed the sky with the panoramic camera and monitored dust on the panoramic camera mast assembly.

Sol 1516: (April 8, 2008): Spirit acquired column 8, part 2 of the Bonestell panorama and surveyed the horizon with the panoramic camera.

Like a calm after the recent Martian dust storms, atmospheric dust above Spirit's overwintering site has reached the lowest levels the rover has seen since arriving on Mars. To be sure, sunblocking dust that has settled on the rover's solar panels and low-angle winter sunlight have combined to reduce Spirit's energy levels. But clear skies mean more sunlight penetrates the atmosphere, making rover planners optimistic that Spirit will have a slim but adequate amount of energy to survive until Martian spring.

Earlier estimates predicted a near-starvation energy diet for Spirit during the darkest days of winter. The coming winter solstice, the peak of Martian winter, will be June 25, 2008. To conserve energy, Spirit may have to disable some heaters and curtail communications and other activities, but is expected to be able to conduct limited scientific investigations.

Solar-array energy during the past week has varied between 244 watt-hours and 254 watt-hours, averaging 249.5 watt-hours for the period (100 watt-hours is the amount of energy needed to light a 100-watt bulb for one hour). Tau, the measure of atmospheric dust, has averaged 0.2, varying by only a few hundredths. The dust factor has been nearly constant at 0.36 (meaning 36 percent of the sunlight reaching the arrays penetrates the dust layer to make electricity). A low Tau is good; a low dust factor is bad.

Because dust is constantly settling out from the Martian atmosphere onto the solar arrays, Tau and the change in the dust factor are related. When Tau is high, the dust factor rapidly decreases as dust from the atmosphere rains onto the arrays. When Tau is low (as it is now), the atmosphere carries less dust and the dust factor decreases more slowly. The clearer atmosphere doesn't affect dust already on the solar arrays, but it does affect the rate at which new dust is added.

The atmosphere above the Spirit site is remarkably clear at present and Tau has been as low as 0.170 -- the lowest seen by Spirit in the entire mission. Not surprisingly, the dust factor has been virtually unchanged.

Spirit also analyzed material on the external capture magnet. Spirit has several magnets of which two, the capture and filter magnets, are mounted at the front of the solar array. The capture magnet is relatively strong, the filter magnet only half as strong.

Viking data from the 1970s showed that Martian dust was slightly magnetic, comprising 1 to 7 percent magnetic material. Spirit's filter and capture magnets winnow the dust for this material. The capture magnet, being stronger, gathers all magnetic materials while the filter magnet retains only the most magnetic particles. Using the alpha-particle X-ray spectrometer, Spirit can determine the chemical composition of the captured particles. The observations will help scientists ascertain whether the magnetic material is uniform or has more than one constituent. The dust composition provides insight into whether the magnetic material is the product of weathering in the presence of water or weathering of dry bedrock.

Spirit continued to scale back the frequency of afternoon communications with the Odyssey orbiter to save energy. Overhead passes by Odyssey happen late in the day when little solar energy is available, requiring the use of significant battery power. By deleting some of the passes, Spirit can conserve energy acquired earlier in the day to provide power for subsequent science observations. The downside is that fewer passes slow the rate at which pictures and other data can be downlinked to Earth.

Spirit continued work on the Bonestell (Bon-ES-tell) panorama, a high-resolution, 360-degree mosaic of images divided into wedges (columns) spanning roughly 5 compass degrees and extending from near the rover to just above the horizon. Each column typically has three or four separate images or "parts." The panorama is named for Chesley Bonestell (1888-1986), considered the "father of modern space art."

Spirit is healthy and all subsystems are performing as expected.

Sol-by-sol summary

To conserve energy, mission planners have restricted the number of sols on which Spirit receives direct-from-Earth instructions via the rover's high-gain antenna and transmits data to Earth via the Odyssey orbiter. Spirit continues, on a daily basis, to monitor atmospheric dust levels with the panoramic camera, check for drift (changes with time) in the miniature thermal emission spectrometer, and survey the sky and ground with the instrument. In addition, during the past week, Spirit completed the following activities:

Sol 1498 (March 20, 2008): Spirit placed the alpha-particle X-ray spectrometer on the capture magnet, took images with the hazard avoidance cameras, took images with the navigation camera for lossless-compression visual odometry, and relayed data to Odyssey.

Sol 1499: Spirit acquired column 4, part 2 of the full-color Bonestell panorama, using all 13 filters of the panoramic camera.

Sol 1500: Spirit acquired column 4, part 3 of the full-color Bonestell panorama, using all 13 filters of the panoramic camera.

Sol 1501: Spirit acquired column 5, part 1 of the full-color Bonestell panorama and relayed data to Odyssey during the orbiter's afternoon pass.

Sol 1502: Spirit took six movie frames in search of clouds with the navigation camera and acquired column 5, part 2 of the Bonestell panorama. Using the alpha-particle X-ray spectrometer, Spirit acquired data on the elemental composition of magnetic particles on the external capture magnet.

Sol 1503 (March 26, 2008): Spirit acquired column 5, part 3 of the Bonestell panorama and relayed data to Odyssey. Plans for the following morning called for Spirit to acquire super-resolution images of a rock target informally named "Roger_Zelazny" (after the science fiction author) with the panoramic camera.

Seasons are about twice as long on Mars as on Earth and are offset relative to Earth because Mars takes about twice as long to complete one orbit around the Sun. At Spirit's location, the fall equinox -- the start of fall, when night and day are equal in length -- arrived Dec. 12, 2007. The winter solstice -- the time of year with the shortest day -- will arrive June 25, 2008.

Solar array energy has varied from 244 watt-hours to 256 watt-hours, averaging 250.4 watt-hours for this period (100 watt-hours is the amount of energy needed to light a 100-watt bulb for one hour). Tau, the measure of atmospheric dust, has averaged 0.16, varying by only a hundredth. The dust factor has been nearly constant at 0.35, meaning 35 percent of the sunlight reaching the arrays penetrates the dust layer to make electricity. A low Tau is good because it means the skies are fairly clear; a low dust factor is bad because it means the solar arrays are coated with a fair amount of dust.

Astronomers use the symbol L(s) -- pronounced L-sub-s -- to denote how far Mars has progressed in its orbit around the Sun. If you imagine looking down at the solar system, with the Sun in the middle and Mars orbiting around it, L(s) gives the location of Mars. By definition, L(s) = 0 degrees when the Sun crosses the Martian equator. This is the first day of Martian spring, the vernal equinox, when night and day are equal in length, in the northern hemisphere. It's also the first day of fall, the autumnal equinox, in the southern hemisphere. At Spirit's location in Mars' southern hemisphere, the season is currently mid- to late fall, and L(s) is about 55 degrees, roughly equivalent to Nov. 17 in Earth's northern hemisphere and May 18 in Earth's southern hemisphere. L(s) will equal 90 degrees at the time of the winter solstice.

Spirit is healthy and all subsystems are performing as expected.

Sol-by-sol summary

To conserve energy, mission planners have restricted the number of sols on which Spirit receives direct-from-Earth instructions via the rover's high-gain antenna and transmits data to Earth via the Odyssey orbiter. Spirit continues, on a daily basis, to monitor atmospheric dust levels with the panoramic camera, check for drift (changes with time) in the miniature thermal emission spectrometer, and survey the sky and ground with the instrument. In addition, during the past week, Spirit completed the following activities:

Sol 1505: Upon awakening, Spirit took spot images of the sky for calibration purposes with the panoramic camera and acquired column 6, part 1 of the full-color "Bonestell panorama" using all 13 filters of the panoramic camera. The rover also recharged the battery.

Sol 1506: Spirit acquired column 6, part 2 of the Bonestell panorama and monitored dust on the panoramic-camera mast assembly. Spirit looked at the miniature thermal emission spectrometer for calibration purposes, acquired microscopic images of the solar panel, and acquired images of the external magnets, which capture magnetic dust particles, using the panoramic camera.

Sol 1509: Spirit surveyed the sky at high Sun with the panoramic camera and completed a "runout" of previously loaded activities after not being able to receive new instructions from Earth. The rover recharged the battery and relayed data to Odyssey.

Sol 1510: (April 2, 2008): Spirit acquired a 1-by-1-by-3 stack of microscopic images of a soil target known informally as "Arthur_C_Hammon" and placed the alpha-particle X-ray spectrometer on the soil target. Plans for the following morning called for Spirit to acquire column 7, part 2 of the full-color Bonestell panorama.

Daily Update - 4/7/08Opportunity Continues Reading the Story in the Rocks
Opportunity Status for sol 1471-1477

Opportunity has finished grinding into the surface and acquiring microscopic images of a rock target informally named "Gilbert," at the bottom of the alcove inside "Victoria Crater" known as "Duck Bay." The rover is in the middle of a campaign to study the composition of the exposed interior of the rock using both the Mössbauer and alpha-particle X-ray spectrometers.

Some time next week, Opportunity is expected to begin driving toward the spectacular promontory in the crater rim known as "Cape Verde" for some close-up imaging.

Because of Opportunity's tilt inside the crater relative to the path of the Mars Odyssey orbiter as it travels across the Martian sky, Opportunity has had difficulty relaying data via UHF links to Odyssey. In the afternoon of Martian day, or sol, 1473 (March 16, 2008), sending data at a rate of 128 kilobits per second, Opportunity returned only 9.5 megabytes of data. On sol 1475 (March 18, 2008), transmitting data at a rate of 32 kilobits per second, Opportunity returned only 3.4 megabytes of data. The rover made up for lost time, however, transmitting 129 megabytes and 91 megabytes on sols 1474 (March 17, 2008) and 1476 (March 19, 2008), respectively.

Power levels continue to drop as expected for the winter season.

Sol-by-sol summary

In addition to receiving instructions directly from Earth via the rover’s high-gain antenna, relaying data to Earth via the UHF antenna on the Mars Odyssey orbiter, and measuring atmospheric dust with the panoramic camera, Opportunity completed the following activities:

Sol 1471 (March 14, 2008): Opportunity acquired data about iron-bearing minerals in a rock target known as "Dorsal New" using the Mössbauer spectrometer. The rover acquired part 10 of the super-resolution panorama of the rim of Victoria Crater, known as the rimshot, using the panoramic camera.

Sol 1472: Opportunity retracted the robotic arm, acquired full-color images of "Dorsal" using all 13 filters of the panoramic camera, and moved the robotic arm back into position to place the rock abrasion tool above Dorsal New. The rover then completed a grind-scan maneuver with the rock abrasion tool to locate the surface of the rock target. Opportunity also surveyed the sky and the horizon with the panoramic camera, acquired parts 11 and 12 of the super-resolution rimshot of Victoria Crater with the panoramic camera, scanned the sky for clouds with the navigation camera, and took spot images of the sky for calibration purposes with the panoramic camera.

Sol 1473: Opportunity acquired parts 13 and 14 of the super-resolution rimshot of Victoria Crater with the panoramic camera, measured argon gas in the Martian atmosphere with the alpha-particle X-ray spectrometer, and took images of the sky (known as "sky flats") for calibration purposes with the navigation camera.

Sol 1474: Opportunity monitored dust on the panoramic-camera mast assembly and surved the horizon with the panoramic camera.

Sol 1475: Opportunity ground into the surface of Dorsal New with the rock abrasion tool, swung the robotic arm out of the way, and took panoramic-camera images of the freshly ground surface.

Sol 1476: Opportunity acquired movie frames in search of clouds with the navigation camera and took spot images of the sky with the panoramic camera.

Sol 1477 (March 20, 2008): Opportunity acquired a 2-by-2-by-5 stack of microscopic images, along with eight extra microscopic images, of the freshly abraded rock surface, and placed the Mössbauer spectrometer on the target for further study.

Spirit is feeling the strain of juggling activities on Mars in the face of declining power levels as the winter Sun sinks lower on the horizon. After acquiring compositional data from a rock target informally named "Wendell Pruitt," Spirit had to wait a few sols (Martian days) to have enough energy to conduct atmospheric studies and move the robotic arm out of the way for a panoramic-camera portrait of a rock target known as "Freeman." First, the rover had to make a "phone call" to Earth to correct for drift -- changes in time -- in the spacecraft clock.

When Spirit phones home using a direct-to-Earth, X-band communications link, the rover's transmitter has to be running, which requires a fair amount of energy. During more typical, direct-from-Earth communications, only the rover's receiver has to be on. To set the spacecraft clock, Spirit transmits a data product called a time packet. The time packet is used to synchronize the rover's clock back to Earth time (also known as Universal Time). A previous attempt to relay the time packet was unsuccessful, causing Spirit's clock to be off by as much as a minute and a half.

In addition to resetting the clock, Spirit completed a light schedule of activities on sols 1493-1494 (March 15-16, 2008). By sol 1496 (March 18, 2008), Spirit had generated enough solar power to proceed with measurements of argon gas in the Martian atmosphere and studies of the Freeman rock target. Interspersed with those activities, Spirit continued to work on the "Bonestell panorama" and take panoramic-camera images of a target dubbed "C.S. Lewis." The rover spent sols 1492, 1494, and 1497 (March 14, 16, and 19, 2008) recharging the battery, conducting only minimal science activities, and storing data for later transmission to Earth.

Spirit continued to have difficulty receiving spacecraft commands via the rover's high-gain, X-band, dish antenna as a result of the mast that holds the panoramic and navigation cameras getting in the way and partially obscuring the signal. To help address this challenge, rover planners had Spirit complete a self-assessment to see if the rover could independently recognize an occlusion of the high-gain signal and respond by swiveling the high-gain antenna to a different position. The self-assessment, on sol 1493 (March 15, 2008), was successful. Spirit used the technique prior to an actual uplink session on sol 1496 (March 18, 2008), when the rover's handlers were expecting a particularly severe occlusion. The activity was successful and the uplink did not appear to be impeded in any way. Currently, this activity involves having the rover use a temporary parameter that then goes away when the rover shuts down for a nap. Rover planners are considering making the temporary parameter permanent.

Looking forward, Spirit will go increasingly into "hibernate" mode as the Sun continues to dim. Rover planners predict Spirit will be able to conduct science activities until about late April.

Spirit is healthy and all subsystems are performing as expected. The latest available power readings from sol 1496 (March 18, 2008) showed power at 249 watt-hours (100 watt-hours is the amount of energy needed to light a 100-watt bulb for one hour). Spirit has no plans to move before the next Martian spring and is hard at work accomplishing as much as possible before power levels drop to a point that temporarily precludes use of the scientific instruments on the rover's arm.

Sol-by-sol summary

To conserve energy, mission planners have restricted the number of sols on which Spirit receives direct-from-Earth instructions via the rover's high-gain antenna and transmits data to Earth via the Odyssey orbiter. Spirit continues, on a daily basis, to monitor atmospheric dust levels with the panoramic camera, check for drift (changes with time) in the miniature thermal emission spectrometer, and survey the sky and ground with the instrument. In addition, during the past week, Spirit completed the following activities:

Sol 1495: In the morning, Spirit acquired column 3, part 1 of the full-color Bonestell panorama, using all 13 filters of the panoramic camera. Spirit positioned the alpha-particle X-ray spectrometer to measure argon gas in the Martian atmosphere. The rover took a single-frame image with the navigation camera. After communicating with Odyssey, Spirit measured argon with the alpha-particle X-ray spectrometer.

Sol 1496: Spirit monitored dust accumulation on the rover mast and acquired column 3, part 3 of the full-color Bonestell panorama. The rover acquired full-color images, using all 13 filters of the panoramic camera, of the Freeman rock target.

Sol 1497 (March 19, 2008): Spirit looked for changes in the "El Dorado" dune field with the panoramic camera and acquired column 4, part 1 of the Bonestell panorama. The rover recharged the battery. The following morning, Spirit was to acquire movie frames in search of clouds with the navigation camera, acquire super-resolution, panoramic-camera images of a target dubbed "C.S. Lewis half," and survey the horizon with the panoramic camera.

Opportunity is wrapping up its scientific investigation of the outcrop exposure known as "Gilbert_A" at the bottom of the alcove known as "Duck Bay," the lowest traversable portion of the crater's interior. Duck Bay is a recess in the walls of "Victoria Crater."

Opportunity performed a dental self-examination of teeth in the rover's rock abrasion tool on Sol 1482 (March 25, 2008). Images of the grinding bit, taken with the hazard avoidance cameras, showed no appreciable wear since the last measurement on sol 1443 (Feb. 14, 2008). In fact, the rover's handlers saw a slight increase rather than decrease in bit height, highlighting the uncertainty inherent in the bit measurement technique. Indeed, the calculated 32 percent of grinding material left is subject to a 39-percent relative error, resulting in an absolute error of 12 percent (based on a statistical calculation, 0.32 * 0.39 = 12). Unfortunately, there is no clear way to reduce the error in bit measurement.

Opportunity is healthy and all subsystems are operating as expected. Energy is currently around 360 watt-hours (100 watts is the amount of energy needed to light a 100-watt bulb for 1 hour). Tau measurement of opacity caused by atmospheric dust is 0.68 (a Tau of zero would correspond to a perfectly clear sky). The dust factor is 0.679, meaning that about 68 percent of sunlight reaching the solar arrays penetrates the coating of dust to generate electricity.

Next week, Opportunity is scheduled to drive toward the promontory known as "Cape Verde" for a better look at the rocks exposed in the crater walls.

Sol-by-sol summary

In addition to receiving morning instructions directly from Earth via the rover’s high-gain antenna, relaying data to Earth each evening via the UHF antenna on the Mars Odyssey orbiter, and completing atmospheric observations that included measuring atmospheric dust with the panoramic camera, monitoring dust accumulation on the rover mast, and scanning the sky for clouds with the navigation camera, Opportunity completed the following activities:

Sol 1478 (March 21, 2008): Opportunity spent 12 hours acquiring data from Gilbert with the Mössbauer spectrometer. The rover completed a survey at high Sun with the panoramic camera and went into a mini-deep sleep.

Sol 1479: Opportunity spent 12 hours acquiring data from Gilbert with the Mössbauer spectrometer. The rover took thumbnail images of the sky for calibration purposes with the panoramic camera and went into a mini-deep sleep.

Sol 1480: Opportunity spent 5 hours acquiring data from Gilbert with the Mössbauer spectrometer and took full-color images, using all 13 filters of the panoramic camera, of the backslope to the left of the Gilbert area. The rover acquired images of the rock target dubbed "Lyell Oxford" and surveyed the horizon with the panoramic camera. The rover went into a deep sleep.

Sol 1481: Opportunity spent 7 hours acquiring data from Gilbert with the alpha-particle X-ray spectrometer and took images of Lyell Oxford with the panoramic camera. The rover took six movie frames spaced at regular intervals in search of clouds with the navigation camera and went into a mini-deep sleep.

Sol 1482: Opportunity took a microscopic image of the hole ground into Gilbert with the rock abrasion tool and completed a survey of the grinding bit on the tool. Opportunity spent 8 hours integrating data from Gilbert with the Mössbauer spectrometer and went into a mini-deep sleep.

Sol 1483 (March 26, 2008): Opportunity spent 7 hours integrating data from Gilbert with the Mössbauer spectrometer and went into a deep sleep.

Spirit continued work on the "Bonestell panorama," a full-color, 360-degree view of the rover's surroundings from its overwintering perch on the north-facing edge of "Home Plate." Spirit acquired images for the panoramic mosaic on sols 1478, 1479, 1480 and 1483 (Feb. 29, March 1-2, and March 5, 2008). By the time the final product is ready, the rover will have completed an estimated 60 separate pointings of the panoramic camera in all different directions. Rover planners have nicknamed the panorama in honor of Chesley Bonestell (1888-1986), considered the father of modern space art.

Spirit has also been engaged in efforts to brush away dust from a rock target known as "Wendell Pruitt." The rover used the rock abrasion tool to brush the surface on sol 1479 (March 1, 2008), but the brushing cleared only about half the expected area. On the basis of the results, the rover's handlers adjusted the command sequence to have Spirit perform a "grind scan" to locate the surface of Wendell Pruitt on sol 1482 (March 4, 2008). The goal of this maneuver was to get the rock abrasion tool in place for another attempted brushing, scheduled for sol 1484 (March 6, 2008).

Spirit is healthy and all subsystems are performing as expected.

Sol-by-sol summary

To conserve energy, mission planners have restricted the number of sols on which Spirit receives direct-from-Earth instructions via the rover's high-gain antenna and transmits data to Earth via the Odyssey orbiter. Spirit continues, on a daily basis, to monitor atmospheric dust levels with the panoramic camera, check for drift (changes over time) in the miniature thermal emission spectrometer, and survey the sky and ground with the instrument. In addition, during the past week, Spirit completed the following activities:

Sol-by-sol summary

To conserve energy, mission planners have restricted the number of sols on which Spirit receives direct-from-Earth instructions via the rover's high-gain antenna and transmits data to Earth via the Odyssey orbiter. Spirit continues, on a daily basis, to monitor atmospheric dust levels with the panoramic camera, check for drift (changes over time) in the miniature thermal emission spectrometer, and survey the sky and ground with the instrument. In addition, during the past week, Spirit completed the following activities:

Sol 1478 (Feb. 29, 2008): Spirit acquired column 1, part 2 of the full-color, panoramic camera images, using all 13 filters of the camera, that will make up the Bonestell panorama. Spirit also recharged the batteries.

Sol 1479: Using the wire brush on the rock abrasion tool, Spirit brushed the surface of Wendell Pruitt. The rover acquired a single-frame, lossless-compression (highly detailed) image of the area in front of the rover using the navigation camera. Spirit relayed data at UHF frequencies to NASA's Odyssey orbiter for transmission to Earth.

Sol 1480: Spirit acquired column 1, part 3 of the Bonestell panorama and measured argon gas in the Martian atmosphere with the alpha-particle X-ray spectrometer.

Sol 1481: Spirit acquired column 2, part 1 of the Bonestell panorama, and recharged the batteries.

Sol 1482: Spirit acquired an image with the panoramic camera pointing south, then completed "Grind Scan2" of the surface of "Wendell Pruitt." The rover acquired a single-frame, lossless-compresson image of the area in front of the spacecraft with the navigation camera. Spirit relayed data at UHF frequencies to NASA's Odyssey orbiter for transmission to Earth.

Sol 1483 (March 5, 2008): Early in the day, Spirit acquired a super-resolution image of the target nicknamed "FredericBrown half" with the panoramic camera. The rover recharged the batteries. The following morning, Spirit was to acquire full-color, panoramic camera images of column 2, part 2 of the Bonestell panorama.

Odometry

As of sol 1482 (March 4, 2008), Spirit's total odometry remained at 7,528.07 meters (4.68 miles).

Opportunity is healthy and all subsystems are performing as expected. Solar array energy rose slightly (approximately 12 watt-hours) during the past week despite a slight increase in Tau, the measure of dust in the atmosphere. Then, on Sol 1462 (March 4, 2008), energy plunged about 19 watt-hours despite a drop in Tau. The dust factor, a measure of the amount of sunlight penetrating dust on the arrays, remained virtually unchanged at 0.72 (meaning 72 percent of sunlight made it through the layer of dust to generate electricity).

During the same time period, power went up to 432 watt-hours, then dropped to 419 watt-hours. The week before, it had declined from about 440 watt-hours to 415 watt-hours (100 watt-hours is the amount of energy needed to light a 100-watt bulb for one hour). Nothing in the environment explains this. Mars is in late fall at the Opportunity site and moving toward winter, with the Sun sinking slightly lower each sol (Martian day). The rover hasn't moved or changed orientation. Tau and dust factor have been relatively steady. So why did power increase, then decrease?

During the previous week, Opportunity used its batteries. A lot. As the batteries discharged, their voltage dropped. Because power is just the product of the voltage and the solar array current, for a given amount of sunlight, the power is lower when recharging a discharged battery than a more fully charged battery. Opportunity's batteries were only about half-charged at the start of the week, bringing energy down a bit. The rover then recharged the batteries and energy went up. Opportunity then dipped into the battery again and energy went back down.

One reason for the increase in energy during the week was that Opportunity didn't complete all of the tasks rover handlers had planned because of a transmitter failure in NASA's Deep Space Network. This network is a collection of big dish antennas that talk and listen to spacecraft, including the Mars Exploration Rovers. Engineers send new plans, called sequences, to the rovers using the Deep Space Network. On sol 1458 (Feb. 29, 2008), they attempted to send plans to Opportunity for sols 1458-1460 (Feb. 29-March 2, 2008), giving instructions for work to be done over the weekend. When the transmitter failed and could not be immediately repaired, the rover repeated a section of the plan for sol 1457 (Feb. 28, 2008) called the "runout."

Each plan controls the rover for a single sol. At the end of the plan, the on-board computer tries to "handover" to the next day's plan. If the next day's plan isn't there, the existing plan continues running with a limited and standardized set of generic observations. In this case, the sol 1457 plan executed its runout for sols 1458, 1459 and 1460 (Feb. 29, March 1, and March 2, 2008).

Of course, there isn't room for an infinite runout, so at the end of the third sol, the rover usually executes a sequence known as "drop into automode." Automode means the plan has ended and is no longer controlling the rover. At that point, the rover is on its own and follows instructions programmed into its flight software for staying healthy and listening for further commands. If there's enough sunlight to power its systems, the rover wakes up, honors any preprogrammed communication windows, and shuts down if either the "up-too-long" limit is reached or the solar arrays aren't generating enough power, whichever comes first.

Because the runout didn't require as much power as the originally planned activities, Opportunity's batteries charged a bit more than expected, causing energy levels to rise.

Opportunity successfully tested communications with the European Space Agency's Mars Express Orbiter, which relays data to Earth much like NASA's Mars Odyssey orbiter, on sol 1461 (March 3, 2008). This and similar demonstrations are aimed at helping NASA's Phoenix mission, now en route to Mars, during entry, descent and landing in late May, 2008.

Opportunity also performed a "quick fine attitude" calibration. This is a procedure to hone the performance of a device called the inertial measurement unit that measures changes in orientation (yaw, pitch and roll). Like all gyroscopes, the unit drifts slightly with time and must be recalibrated every so often. During this procedure, a set of commands tells the panoramic camera to look for the Sun, identify where it is, compute the difference between its predicted and actual position, and update the inertial measurement unit accordingly. The correction from this particular recalibration was about 2.25 degrees, slightly larger than usual but not hugely so.

Sol-by-sol summary

In addition to receiving instructions directly from Earth via the rover’s high-gain antenna, relaying data to Earth via the UHF antenna on the Mars Odyssey orbiter, and measuring atmospheric dust with the panoramic camera, Opportunity completed the following activities:

Sol 1457 (Feb. 28, 2008): Opportunity placed the microscopic imager over a rock target known as "Dorsal" and acquired a 2-by-1-by-20 stack of stereo (3-D) microscopic images. The rover placed the alpha-particle X-ray spectrometer on Dorsal and spent about 6 hours acquiring data with the instrument, then went into a mini-deep sleep.

Sol 1458: Opportunity was unable to complete the day's activites after a Deep Space Network transmitter outage. Items not completed included spot images of the sky, navigation camera measurements of atmospheric dust, movie frames in search of clouds, a "quick get fine attitude," acquisition of data with the Mössbauer spectrometer, and transmission of data to Odyssey.

Sol 1459: Following the previous sol's transmitter outage, Opportunity was unable to execute plans to acquire a 2-by-1 mosaic of panoramic camera images of an alcove in the rim of "Victoria Crater" known as"Cabo Frio," a 5-by-1 mosaic of rearward-looking navigation camera images, and Mössbauer spectrometer data. Opportunity was also not yet able to test communications with Mars Express or transmit data to Odyssey.

Sol 1460: Following the transmitter outage on Sol 1458, Opportunity was not able to execute plans to acquire full-color images using all 13 filters of the panoramic camera of a target dubbed "Jin," survey the horizon with the panoramic camera, acquire data with the Mössbauer spectrometer, take full-color images of the hole created with the rock abrasion tool in the rock layer known as "Lyell," or acquire six movie frames in search of clouds.

Sol 1461: With Deep Space Network transmissions restored, Opportunity suspended the Mössbauer spectrometer over Dorsal to set its position before moving the robotic arm out of the field of view of the hazard avoidance cameras, executed a "quick fine attitude," and acquired images for mapping and modeling the terrain with the front hazard avoidance cameras. The rover placed the Mössbauer spectrometer on Dorsal and spent approximately 9 hours collecting data with the instrument. Opportunity successfully tested communications with Mars Express.

Sol 1462 (March 4, 2008): Opportunity acquired the previously planned 2-by-1 mosaic of images of Cabo Frio with the panoramic camera and 8-by-1 mosaic of rearward-looking images with the navigation camera. The rover switched tools from the Mössbauer spectrometer to the alpha-particle X-ray spectrometer and, after communicating with Odyssey, collected roughly 7 hours worth of compositional data with the instrument. The rover went into a mini-deep sleep. The following morning, Opportunity was scheduled to take the previously planned, full-color, panoramic-camera images of the hole ground into Lyell.